It means you are guaranteed the category indicated but not a specific room in that category at the time of reservation. I'm sure someone will be able to give you info on documents.
GTY means that the particular category you requested is overbooked at that time but DCL will guarantee that you will at least have that category or possibly a higher one (never lower). When they adjust inventory a cabin in your category may become available for you and it will be assigned. If not, then you will be assigned a higher category. DCL does a lot of juggling of cabin inventory in the weeks before the cruise so that is why you would not find out your cabin number until you check in. But, if you call about a week before and inquire they may be able to tell you where you have been assigned.
Remember, you will never be put in a lower category than what you booked. It also does not mean that you will get a "bad" location room...we have booked a few time at GTY status and have always gotten great location rooms.
You will still get your document package like everyone else, you may just not have your assigned cabin listed yet in them.
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